The present invention relates generally to a hermetic compressor and, more particularly, to a compressor having a reciprocating piston including a suction valve assembly located therein.
In general, hermetic compressors comprise a hermetically sealed housing having a compressor mechanism mounted therein. The compressor mechanism may include a crankcase or a cylinder block defining a compression chamber in which gaseous refrigerant is compressed and subsequently discharged.
A disadvantage to prior compressor designs is that there is always a certain volume left in the cylinder when the piston is at top dead center position. This volume of gas is repetitively compressed and re-expanded during the reciprocation of the piston. Reexpansion volume causes a loss of energy efficiency in a compressor.
In prior art compressors utilizing valve-in-piston designs disclosed, for example, in U.S. Pat. No. 2,117,601 and U.S. Pat. No. 4,834,632, the suction valve is mounted adjacent the top surface of the piston head and is axially reciprocatingly displaceable in the space limited by the piston top surface and the valve retainer. The separate spacer washer, located in the same limited space, guides the movement of the valve and defines the possible amount of valve lift. An overlapping screw head or washer retains movement of the ring type valve and, simultaneously clamps the spacer washer between screw head and the piston head top surface. Due to the fact that the spacer washer is slightly thicker than the valve, the valve is allowed limited axial movement beneath the screw head.
Because of the location of the suction valve above the surface at the piston top in the prior art valve-in-piston design, space has been provided in the valve plate to accommodate the valve, and its guiding and retaining members. This increases the clearance volume, complicates assembly of the valving system, and increases the manufacturing cost of the compressor.
The location of the circular retainer in the vicinity of the central part of the valve, while the gas dynamic forces are applied to the peripheral part of the ring valve, localize forces acting at the center thereof and drastically increase polar inertia momentum of the valve. As the valve strikes the retainer, a relatively large amount of stress is placed on the retainer that may cause damage, due to the forces concentrated in the central part and/or due to accumulation of wear due to repeated collisions of the parts.
Use of ring type valves made from steel are common in prior art compressors. The ability of such valves steel to resist the stresses created by repeated bending (flexural stress) and impact stresses caused by colliding of the valve with the seat/stop is one of the essential properties of prior art valve steel. As shown in numerous studies, a valve material with higher damping characteristics will absorb induced stress peaks more efficiently, minimize valve damage, and reduce a noise generating by such impacts.
Further, gas passages in prior art suction valves have normally only included a single outside gas passage. By limiting the valves to a single outside gas passage, throttling occurs reducing compressor efficiency.
A plastic valve disk is known from U.S. Pat. Nos. 4,955,796 and 5,106,278. This plastic valve has been mounted on the top of the piston for limited, axial floating motion sufficient to close or open gas passages located in the top of the piston. Such a design of the plastic valve reduces, to some degree, valve flexural stress, but still includes a source of concentrated impact stress due to the central location of the retaining means. Another disadvantage of such a plastic valve disk is the use of the bridging cover in the central part of the valve, which is affixed to the disk body by screws and plastic welding. It is noted that the excess flexing of the plastic material by itself presents a problem. The central bridging plastic part requires some type of re-enforcement due to the tendency for the thin plate, suspended at an edge, to buckle or warp under influence of changing gas pressure.
An objective of the proposed invention is to provide a reliable suction valve system with an improved design for gas passages which will increase effective valve flow area and minimize the pressure drop and cylinder clearance volume. The present invention also reduces turbulence formation, decreases noise generated by the valving system and is inexpensive to manufacture.